572 



SCIENCE 



[N. S. Vol. XXVII. No. 693 



Some Cases of Excessive Damping of Tor- 

 sional Vibrations: K. E. Guthe, Iowa 

 State University. 



The decrease of the logarithmic decre- 

 ment with the amplitude, frequently ob- 

 served in torsional vibrations, is usually 

 extremely small. It is considered as close- 

 ly connected with the elastic after-effect. 

 "Wires of platinum-iridium which are prac- 

 tically free from such after-effect have not 

 alone a large logarithmic decrement, but 

 show also a decided decrease of decrement 

 as well as period with decreasing amplitude. 

 This is especially pronounced in a 40 per 

 cent, platinum-iridium wire whose loga- 

 rithmic decrement decreased from 0.0137 

 to 0.0025, while the amplitudes decreased 

 from 5.7 to 0.85 degrees. The correspond- 

 ing change in the period was from 7.350 

 to 7.175 seconds. The decrease in ampli- 

 tude is nearly proportional to the square 

 of the amplitude. With different moments 

 of inertia suspended from the wire the 

 values of the decrement remained the same 

 for the same amplitudes. 



Similar effects, though less pronoimced, 

 were observed with wires containing a 

 smaller percentage of iridium and in drawn 

 wires of other materials. It was attempted 

 to explain the phenomena by the assump- 

 tion that the disappearance of the elastic 

 after-effect is very rapid. 



The increase of the logarithmic decre- 

 ment upon drawing was explained by 

 Beilby's theory of the effect of mechanical 

 hardening. A carbon filament was shown 

 to have a large decrement; the electrolytic 

 deposition of hydrogen upon palladium in- 

 creased the logarithmic decrement fivefold. 

 In conclusion, it was pointed out that the 

 conditions under which a wire is annealed 

 by heating greatly influence its elastic 

 properties. 



F. N. Cole, 

 Secretary 

 (To he concluded) 



THE CARNEGIE INSTITUTION OF 

 WASHINGTON "■ 



Repeering to the individual reports of 

 the heads of departments for a more ade- 

 quate account of the year's work on the 

 numerous and diverse fields of depart- 

 mental activity, the following summary 

 may suffice to show the trend of current 

 progress. 



DEPARTMENT OF BOTANICAL RESEARCH 



This department is engaged on a series 

 of problems whose elucidation can not fail 

 to be of the greatest interest and value, 

 whether applied to the restricted field of 

 botany or to the broader domain of biology. 

 By means of observation, experiment and 

 measurement it is proposed to determine, 

 as nearly as may be, the conditions of de- 

 velopment, growth, distribution, migration 

 and variation of desert plants. Thus, in 

 addition to systematic studies of the forms 

 and distribution of these plants, there must 

 be carried on studies of the factors of tem- 

 perature, rainfall, evaporation, soil mois- 

 ture and anatomical and physiological 

 adaptability. The location of the desei't 

 laboratory in a country affording a wide 

 range of plant forms, as well as a wide 

 range of conditions in altitude, tempera- 

 ture, soil moisture and soil composition, 

 presents unequaled opportunities for such 

 studies. 



Along with these lines of work, the 

 anatomical, physical and physiological re- 

 searches of the department staff have al- 

 ready resulted in noteworthy contributions 

 to biological science. Among these, refer- 

 ence may be made especially to publication 

 No. 81, in which Director MacDougal gives 

 an account of the production of a new 

 species of plant by an application of chem- 

 ical fiuids to the parent plant seeds during 

 the period of germination. This remark- 

 able achievement must be regarded as one 



' From the annual report of the president for 

 1907. 



